According to prior arts, it has been known to obtain SOI including a handle substrate composed of a transparent and insulating substrate and called Silicon on Quartz (SOQ), Silicon on Glass (SOG) and Silicon on Sapphire (SOS), and to obtain an adhered wafer by bonding a transparent wide-gap semiconductor including GaN, ZnO, diamond, MN or the like to a donor substrate such as silicon. SOQ, SOG, SOS and the like are expected for applications such as a projector and high frequency device due to the insulating property and transparency of the handle substrate. Further, the adhered wafer, which is a composite of a thin film of the wide-gap semiconductor and the handle substrate, is expected in applications such as a high performance laser and power device.
Such composite substrate for a semiconductor is composed of a handle substrate and donor substrate, and the handle and donor substrates are generally made of single crystal materials. According to prior arts, it was generally performed a method of forming a silicon layer on a base substrate by epitaxial growth. It has recently developed a method of directly bonding them to contribute to the improvement of performance of a semiconductor device (Patent documents 1, 2 and 3). That is, such handle and donor substrates are bonded through a bonding layer or an adhesive layer or directly bonded with each other.
However, sapphire is expensive. It is thus desired to use a substrate made of a material other than sapphire as the handle substrate for cost reduction. As the development of the bonding technique as described above, it has been proposed various kinds of handle substrates made of materials, other than sapphire, such as quartz, glass and alumina (Patent documents 4, 5, 6 and 7).